Fix pg_identify_object_as_address() with event triggers

Fix pg_identify_object_as_address() with event triggers

Attempting to use this function with event triggers failed, as, since
its introduction in a676201, this code has never associated an object
name with event triggers.  This addresses the failure by adding the
event trigger name to the set defining its object address.

Note that regression tests are added within event_trigger and not
object_address to avoid issues with concurrent connections in parallel
schedules.

Author: Joel Jacobson
Discussion: https://postgr.es/m/3c905e77-a026-46ae-8835-c3f6cd1d24c8@www.fastmail.com
Backpatch-through: 9.6